Acquired immune deficiency syndrome and the developing nervous system

Chemokine release is associated with the protective action of PACAP-38 against HIV envelope protein neurotoxicity

The envelope protein (gp120) of the human immunodeficiency virus produces neuronal cell death in cultures that can be prevented by co-treatment with pituitary adenylate activating peptide-38 (PACAP-38) or chemokines. To investigate the hypothesis that a functional relationship exists between these two protectants, the release of chemokines was measured in rat astrocyte cultures after PACAP-38 treatment. Chemokine analyses were performed by immunoaffinity capillary electrophoresis. Bell-shaped dose-responses for PACAP-mediated release of chemokines into the culture medium were observed with EC(50)'s of 3 x 10(15) M (RANTES: regulated upon activation normal T cell expressed and secreted), 3 x 10(-11) M (MIP-1 beta) and 10(-7)M (MIP-1 alpha). In addition, PACAP-mediated depletion of chemokines from cultured astrocytes exhibited inverted bell-shaped curves, with similar EC(50)'s to those observed for chemokine measurements of the medium. Comparative studies with structurally related peptides (vasoactive intestinal peptide [VIP] and secretin) revealed that PACAP was the most potent secretagogue for RANTES on astrocyte cultures. Gp120-mediated neuronal cell death was prevented by co-treatment with PACAP-38, although the efficacy of protection varied significantly among the gp120 isolates. A bi-model dose-response was observed with EC(50)'s of 3 x 10(-15) and 3 x 10(-11) M. Co-treatment with neutralizing antiserum to RANTES attenuated PACAP-mediated protection from toxicity associated with gp120. In contrast to previous studies with VIP and gp120 toxicity, co-treatment with anti-MIP-1 alpha did not affect PACAP-induced protection. These studies support the hypothesis that PACAP produces neuroprotection from gp120 toxicity, in part, through the release of RANTES and this mechanism is distinct from that observed with VIP.

The human immunodeficiency virus-1 envelope protein gp120 binds through its V3 sequence to the glycine site of N-methyl-D-aspartate receptors mediating noradrenaline release in the hippocampus

Recent results show that the HIV-1 protein gp120 can enhance N-methyl-D-aspartate receptor-mediated release of noradrenaline from CNS nerve endings. We now investigate the mechanism of this action, including the structural determinants of the gp120 effect and the nature of its binding sites. The N-methyl-D-aspartate-evoked release of [3H]noradrenaline from rat hippocampal synaptosomes was potentiated similarly by gp120 and gp160; gp41 was ineffective. The regions of gp120 involved appear to be outside the CD4-binding domain of the protein, because gp120 retained its activity after pretreatment with N-carbomethoxycarbonyl-D-prolyl-D-phenylalanine, a compound known to inhibit binding of gp120 to CD4 receptors. Moreover, sequences of gp120 critical for binding to CD4 did not mimic the effect of gp120. Preincubation of synaptosomes with anti-galactocerebroside antibodies did not affect gp120 activity. The protein effect was retained by peptides mimicking its V3 sequence, including the cyclic V3 "universal peptide" and the linear V3 sequence BRU-C-34-A, but not RP-135 (a central portion of BRU-C-34-A). The block of the N-methyl-D-aspartate-induced [3H]noradrenaline release by 7-chlorokynurenate, an antagonist at the N-methyl-D-aspartate receptor glycine site, was competitively reversed by glycine, by V3 and by BRU-C-34-A. When added with N-methyl-D-aspartate, V3 was three to four orders of magnitude more potent than glycine (EC50 values: about 20 pM and 150 nM, respectively) in enhancing [3H]noradrenaline release. Gp120 did not release glycine or serine from synaptosomes, thus excluding indirect actions through these agents. To conclude, gp120 may act following recognition by its V3 sequence of a high-affinity site possibly coincident with the glycine site of N-methyl-D-aspartate receptors present on hippocampal terminals of noradrenergic neurons. Considering the importance of N-methyl-D-aspartate receptor activation and of noradrenaline in cognitive processes, the effects of gp120 and V3 described here may be relevant to the pathology of AIDS dementia.

A femtomolar-acting neuroprotective peptide

A novel 14-amino acid peptide, with stress-protein-like sequences, exhibiting neuroprotection at unprecedented concentrations, is revealed. This peptide prevented neuronal cell death associated with the envelope protein (GP 120) from HIV, with excitotoxicity (N-methyl d-aspartate), with the beta amyloid peptide (putative cytotoxin in Alzheimer's disease), and with tetrodotoxin (electrical blockade). The peptide was designed to contain a sequence derived from a new neuroprotective protein secreted by astroglial cells in the presence of vasoactive intestinal peptide. The neurotrophic protein was isolated by sequential chromatographic methods combining ion exchange, size separation, and hydrophobic interaction. The protein (mol mass, 14 kD and pI, 8.3 +/- 0.25) was named activity-dependent neurotrophic factor, as it protected neurons from death associated with electrical blockade. Peptide sequencing led to the synthesis of the novel 14-amino acid peptide that was homologous, but not identical, to an intracellular stress protein, heat shock protein 60. Neutralizing antiserum to heat shock protein 60 produced neuronal cell death that could be prevented by cotreatment with the novel protein, suggesting the existence of extracellular stress-like proteins with neuroprotective properties. These studies identify a potent neuroprotective glial protein and an active peptide that provide a basis for developing treatments of currently intractable neurodegenerative diseases.

gp120 as an etiologic agent for NeuroAIDS: neurotoxicity and model systems

The search for an agent that can mediate the symptoms of NeuroAIDS has been directed at gp120, the major envelope protein from HIV. The toxicity associated with gp120 was examined as a model and predictor of the neuropathological and neuropsychiatric manifestations of AIDS. Studies of the neurotoxic effects of purified gp120 on neurons from the rodent CNS cell cultures indicated the following: potent and selective killing of subpopulations of hippocampal neurons; varying potency of gp120s obtained from various HIV isolates; complete and potent protection from gp120 killing action after treatment with peptides related to vasoactive intestinal peptide; and obligatory presence of glia for gp120-related toxicity. Investigations of gp120 treatment of rodents revealed: cortical neurodystrophy with reduced arborizations and swollen processes; delays in developmental behaviors involving motor skills; peptide T prevention or attenuation of the morphological and behavioral deficits/delays produced by administration of gp120; and impairment of learning in the Morris swim maze. In addition, studies of subcutaneously administered, radiolabeled gp120 in neonatal animals demonstrated the presence of toxic fragments of gp120 in the developing brain. With the use of model test systems of non-human derived cell cultures and neonatal rats, we have captured and predicted a number of the morphological and behavioral deficits associated with AIDS. These multi-disciplinary studies of the actions of gp120 and associated fragments in rodents and rodent cells predict that the loss of cognitive and neurological function in patients with AIDS are attributed in part to interference of critical brain functions by the envelope protein, gp120.

Neuropeptides as growth and differentiation factors in general and VIP in particular

During the course of neurodevelopment a large population of neurons die normally (Berg, 1982; Oppenheim et al., 1989). Are neuropeptides involved in the regulation of neuronal survival, maturation, and maintenance? The peptides are an ever growing family of neuroactive agents and this review shall emphasize VIP (vasoactive intestinal peptide [Said and Mutt, 1970; Gozes and Brenneman, 1989]), which has been shown to be involved in maturation, growth, and maintenance of neurons (Brenneman et al., 1985a, 1987, 1988, 1990, 1990b; Brenneman and Eiden, 1986; Brenneman and Nelson, 1986). Comparative actions of other neuropeptides will also be discussed.